1 //=== FileOutputBuffer.h - File Output Buffer -------------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // Utility for creating a in-memory buffer that will be written to a file. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #ifndef LLVM_SUPPORT_FILEOUTPUTBUFFER_H 14 #define LLVM_SUPPORT_FILEOUTPUTBUFFER_H 15 16 #include "llvm/ADT/SmallString.h" 17 #include "llvm/ADT/StringRef.h" 18 #include "llvm/Support/DataTypes.h" 19 #include "llvm/Support/Error.h" 20 #include "llvm/Support/FileSystem.h" 21 22 namespace llvm { 23 /// FileOutputBuffer - This interface provides simple way to create an in-memory 24 /// buffer which will be written to a file. During the lifetime of these 25 /// objects, the content or existence of the specified file is undefined. That 26 /// is, creating an OutputBuffer for a file may immediately remove the file. 27 /// If the FileOutputBuffer is committed, the target file's content will become 28 /// the buffer content at the time of the commit. If the FileOutputBuffer is 29 /// not committed, the file will be deleted in the FileOutputBuffer destructor. 30 class FileOutputBuffer { 31 public: 32 enum { 33 /// set the 'x' bit on the resulting file 34 F_executable = 1, 35 36 /// Don't use mmap and instead write an in-memory buffer to a file when this 37 /// buffer is closed. 38 F_no_mmap = 2, 39 }; 40 41 /// Factory method to create an OutputBuffer object which manages a read/write 42 /// buffer of the specified size. When committed, the buffer will be written 43 /// to the file at the specified path. 44 /// 45 /// When F_modify is specified and \p FilePath refers to an existing on-disk 46 /// file \p Size may be set to -1, in which case the entire file is used. 47 /// Otherwise, the file shrinks or grows as necessary based on the value of 48 /// \p Size. It is an error to specify F_modify and Size=-1 if \p FilePath 49 /// does not exist. 50 static Expected<std::unique_ptr<FileOutputBuffer>> 51 create(StringRef FilePath, size_t Size, unsigned Flags = 0); 52 53 /// Returns a pointer to the start of the buffer. 54 virtual uint8_t *getBufferStart() const = 0; 55 56 /// Returns a pointer to the end of the buffer. 57 virtual uint8_t *getBufferEnd() const = 0; 58 59 /// Returns size of the buffer. 60 virtual size_t getBufferSize() const = 0; 61 62 /// Returns path where file will show up if buffer is committed. 63 StringRef getPath() const { return FinalPath; } 64 65 /// Flushes the content of the buffer to its file and deallocates the 66 /// buffer. If commit() is not called before this object's destructor 67 /// is called, the file is deleted in the destructor. The optional parameter 68 /// is used if it turns out you want the file size to be smaller than 69 /// initially requested. 70 virtual Error commit() = 0; 71 72 /// If this object was previously committed, the destructor just deletes 73 /// this object. If this object was not committed, the destructor 74 /// deallocates the buffer and the target file is never written. 75 virtual ~FileOutputBuffer() {} 76 77 /// This removes the temporary file (unless it already was committed) 78 /// but keeps the memory mapping alive. 79 virtual void discard() {} 80 81 protected: 82 FileOutputBuffer(StringRef Path) : FinalPath(Path) {} 83 84 std::string FinalPath; 85 }; 86 } // end namespace llvm 87 88 #endif 89